This invention relates to novel anti-apoptotic use of human glutaminyl-tRNA synthetase with two consecutive pro-apoptotic mediators, that are ASK1 and Daxx.
Apoptosis is a normal physiologic process that leads to individual cell death. This process of programmed cell death is involved in a variety of normal and pathogenic biological events and can be induced by a number of unrelated stimuli. Changes in the biological regulation of apoptosis also occur and diseases related to aging. Recent studies of apoptosis have implied that a common metabolic pathway leading to cell death may be initiated by a wide variety of signals, inducing hormones, serum growth factor deprivation, chemotherapeutic agents, ionizing radiation and infection by human immunodeficiency virus(HIV).
While apoptosis is a normal cellular event, it can also be induced by pathological conditions and a variety of injuries. Apoptosis is involved in a wide variety of conditions including but not limited to, cardiovascular disease, cancer regression, immunoregulation, viral diseases, anemia, neurological disorders, gastrointestinal disorders, including but not limited to, diarrhea and dysentery, diabetes, hair loss, rejection of organ trnasplants, prostate hypertrophy, obesity, ocular disorders, stress and aging.
Aminoacyl-tRNA synthetases (ARSs) play an essential role in protein synthesis, decoding genetic information into amino acids. These enzymes were generated early in evolution and accumulated a wide range of structural and functional diversity. The structural difference is not only observed between different ARSs but also between the same ARSs of different phylogenetic kingdoms (1). ARSs of higher eukaryotes have adopted many peculiar features in their structure and behavior distinguishable from those of prokaryotes (2-4).
For instance, some ARSs are functionally linked to apoptosis. Human tyrosyl-tRNA synthetase is released from the cell upon apoptosis and split into two distinct pro-apoptotic cytokines (5). The precursor of pro-apoptotic cytokine, EMAPII (endothelial monocyte activating polypeptide II) is associated with the N-terminal non-catalytic extension of arginyl-tRNA synthetase to facilitate aminoacylation (6). The C-terminal cytokine domain of this precursor is released by an apoptotic signal and exerts its pro-apoptotic function (7).
Aminoacyl-tRNA synthetases are the enzymes catalyzing ligation of their cognate amino acids and tRNAs. Human glutaminyl-tRNA synthetase (QRS) consists of the unique N-terminal extension (236 aa) and the C-terminal catalytic domain (539 aa). Here, we found that the N- and C-domains of QRS interacted with pro-apoptotic mediator, Daxx, and its downstream kinase, ASK1 (apoptosis signal-regulating kinase), respectively. The experimental results suggest that QRS may inhibit the ASK1 activity via two different ways. First, its C-terminal domain made direct inhibitory interaction with ASK1. Second, it inhibited the pro-apoptotic interaction between Daxx and ASK1. QRS also blocked the Daxx-ASK1 mediated apoptosis. Thus, QRS plays a regulatory role in apoptosis and thus can be used to control cell death.